Referring to FIG. 1, a conventional locking coupling assembly 4 is shown to include a cylindrical body 41 connected to a female coupling tube (not shown), a male coupling tube 42 inserted into the cylindrical body 41 and fluid-tightly engaged therewith by means of a seal ring 40, and two cam-lock actuating devices 43. Each of the cam-lock actuating devices 43 includes an actuating lever 431, a spring-biased lock bolt 432, and a pull ring 433. The actuating lever 431 is pivotably mounted to a lug 411 of the cylindrical body 41 by a pivot pin 44, and has a cam surface 434 extending into the cylindrical body 41 for engaging an annular grooved surface 421 of the male coupling tube 42 when the actuating lever 431 is at a locking position. The spring-biased lock bolt 432 is movably received in a hole formed in the actuating lever 431 and has an upper end 435 which is biased to be inserted into a locking hole 410 in the cylindrical body 41 for retaining the actuating lever 431 at the locking position. The pull ring 433 is attached to a lower end 436 of the spring-biased lock bolt 432 such that by pulling the pull ring 433, the upper end 435 is moved downwardly to be disengaged from the locking hole 410 so as to permit turning of the actuating lever 431 to an unlocking position, where the cam surface 434 is disengaged from the annular grooved surface 421. Thus, the locking coupling assembly 4 can be used to quickly connect and disconnect two tubular members, such as hoses, pipes, etc.
During displacement of the actuating lever 431 between the locking and unlocking positions, the cam surface 434 of the actuating lever 431 will rub against the annular grooved surface 421 of the male coupling tube 42, which may produce spark, static electricity, or metal powders due to wearing of the cam surface 434 and/or the annular grooved surface 421. As such, the conventional locking coupling assembly 4 cannot be used to connect tubular members for transporting a flammable material or a food material.
To prevent the production of spark, etc., the cam surface 434 of the actuating lever 431 may be roughened using, for example, chemicals to permit a thin layer of polytetrafluoroethylene to be coated over the roughened cam surface 434. However, a bonding force between the polytetrafluoroethylene layer and the cam surface 434 is insufficient, and the polytetrafluoroethylene layer may be delaminated from the cam surface 434 after a period of use.